Field of the Invention
The present invention relates to an image capture apparatus and a method for controlling the same.
Description of the Related Art
Electronic devices having an image capture function, such as digital cameras, mobile phones with a camera, game consoles, and personal computers, typically realize an autofocus function.
Japanese Patent Laid-Open No. 2010-117679 discloses an image sensor including focus detection pixels in which a range of light that is incident on photoelectric conversion areas is controlled by a light-shielding film having openings that are eccentric to the light axes of microlenses provided on the pixels. Because such focus detection pixels each receive outgoing light from a partial region of an exit pupil of a shooting lens, it is possible to obtain a defocus amount of an imaging optical system based on a phase difference between a pair of output waveforms that can be obtained from the focus detection pixels, the focus detection pixels being provided with the light-shielding film having openings that are eccentric in the different directions.
Furthermore, an image sensor in which each pixel includes one microlens and a plurality of photoelectric conversion areas as disclosed in Japanese Patent Laid-Open No. 2013-186201 can also be used to obtain a defocus amount of an imaging optical system based on the same principle. This is because the plurality of photoelectric conversion areas in one pixel receive, via the same microlens, outgoing light from different regions of an exit pupil of an imaging optical system.
Accordingly, autofocus detection of a phase-difference detection method that uses signals obtained from an image sensor, instead of a separate focus detection sensor, is also referred to as image-plane phase-difference detection AF.
Such a focus detection method that uses output signals of photoelectric conversion areas that receives, via a microlens, outgoing light from different regions of an exit pupil of a shooting lens is likely to be affected by vignetting of the shooting lens. Once vignetting of the shooting lens occurred, a pair of output waveforms for use in phase difference detection varies in shape, deteriorating the phase-difference detection accuracy and thus focus detection accuracy. Furthermore, the adverse effect of vignetting on the phase-difference detection accuracy increases with an increase in the defocus amount. This is because, since the larger the defocus amount the lower the contrast, the output waveforms significantly vary in shape due to vignetting.